Image sensors are widely used in digital still cameras, cellular phones, and security cameras, as well as in medical, automobile, and other applications. The technology used to manufacture image sensors, and especially complementary metal-oxide-semiconductor (“CMOS”) image sensors, has continued to advance at great pace, and the demands of higher resolution and lower power consumption have encouraged further miniaturization and integration of image sensors.
Conventional CMOS image sensors use color filter arrays (CFAs) with a set of primary colors such as red, green, and blue (RGB) arranged in what is known as a Bayer pattern. In some embodiments clear pixels, also known as colorless, clear, or panchromatic pixels, can be included in the color filter array to increase the sensitivity of the image sensor. A color filter array that includes clear filters in addition to RGB color filters can be referred to as an RGBC pixel pattern.
Some RGBC patterns increase sensitivity but can suffer from color aliasing. Color aliasing results in the wrong color appearing in an area of the image. For instance, a color such as red or blue can appear in a part of the image that should be green. In another example of color aliasing, a small white line on a black or otherwise dark background that registers on individual pixels will be interpreted as a line containing single pixels of each of the primary colors registered. Color aliasing occurs at least partly due to the alignment of clear filters within an RGBC pattern. Image sensors with clear pixels are more prone to color aliasing because clear pixels do not produce any color information of their own other than the intensity of light.
Color aliasing is a generally undesirable effect caused by using certain color filter array (CFA) patterns with charge-coupled device (CCD) image sensors or CMOS image sensors. It is therefore desirable to design CFA patterns that minimize color aliasing.